Drunkenness is a state characterized by impaired judgment, coordination, and altered perceptions, stemming from the consumption of alcoholic beverages. This condition affects the brain and body, leading to physiological and psychological changes. Understanding the specific molecule responsible for these effects provides insight into the experience of intoxication.
Ethanol The Main Culprit
The molecule primarily responsible for the intoxicating effects of alcoholic beverages is ethanol, also known as ethyl alcohol or grain alcohol. Its chemical formula is C2H5OH.
Ethanol is produced through fermentation, where yeast or bacteria react with sugars in grains, fruits, or vegetables, converting them into ethanol and carbon dioxide. Examples include beer from malted barley, wine from grapes, and vodka from potatoes.
How Ethanol Affects the Brain
Once consumed, ethanol quickly enters the bloodstream and travels to the brain, significantly altering brain chemistry. Its effects on neurotransmitters, chemical messengers that transmit signals between nerve cells, are central to drunkenness.
Ethanol enhances gamma-aminobutyric acid (GABA), the brain’s primary inhibitory neurotransmitter. This leads to a slowing of brain activity, contributing to relaxation, sedation, and reduced anxiety. Increased GABA action can result in symptoms like slurred speech, impaired judgment, and reduced inhibitions.
Ethanol also inhibits glutamate, the brain’s primary excitatory neurotransmitter involved in learning and memory. By blocking its receptors, ethanol impairs cognitive functions and memory formation, contributing to memory lapses and a general slowing of brain processes. Additionally, ethanol affects dopamine pathways, increasing dopamine release in the brain’s reward centers. This surge can contribute to feelings of pleasure and reward associated with alcohol consumption.
The Body’s Response to Ethanol
The liver plays the central role in ethanol metabolism, breaking down most consumed ethanol through a two-step enzymatic process. The primary enzyme, alcohol dehydrogenase (ADH), converts ethanol into acetaldehyde, a highly toxic compound.
Another enzyme, aldehyde dehydrogenase (ALDH), rapidly converts acetaldehyde into less toxic acetate. Acetaldehyde is more toxic than ethanol and causes many unpleasant hangover symptoms like nausea, headaches, and fatigue. The liver metabolizes ethanol at a constant rate, typically one standard drink per hour. If consumed faster, acetaldehyde accumulates, leading to more pronounced toxic effects.
Why People React Differently
Individual responses to ethanol vary significantly due to genetic and environmental factors, influencing how quickly and intensely a person experiences its effects. Body weight and composition play a role, as individuals with more body water dilute ethanol more effectively, leading to lower blood alcohol concentrations. Biological sex also influences processing, as women generally have lower levels of the enzyme ADH and less body water than men, resulting in higher blood alcohol concentrations more quickly. Food in the stomach slows ethanol absorption, delaying and reducing its peak effects.
Genetic variations in ADH and ALDH enzymes significantly impact ethanol and acetaldehyde metabolism. For instance, some people, particularly of East Asian descent, have a less active ALDH2, causing rapid acetaldehyde buildup. This leads to symptoms like facial flushing, nausea, and a rapid heart rate, known as the “alcohol flush reaction,” which can deter heavy drinking. Chronic ethanol exposure can also lead to tolerance, where the brain and body adapt, requiring larger amounts for the same intoxicating effects. This involves changes in neurotransmitter systems and enzyme production.